Thermostats are universally present in dwellings and other temperature-controlled spaces. It is standard practice to mount them on a wall which will allow accurate control of the temperature within the space. They come in a variety of shapes and with a variety of functions. All thermostats do, however, share the feature of having some means for adjusting the temperature set point. The simple electromechanical thermostats typically have a bimetal coil with a free end whose angular orientation controls the temperature setting, typically by shifting the angle of a mercury bulb switch. In some designs, the bimetal coil orientation is controlled by rotating a knob, the famous Honeywell "ROUND" (registered US trademark) being only the most common of these. Thermostats with temperature setting knobs are usually but not always round. There is also another class of thermostats whose setting is lever-controlled. These are usually rectangular. One shape or the other may be preferred for no other reason than personal choice or greater compatibility with the decor of the room on whose wall the thermostat is mounted. It is true that it is easier to implement a larger number of auxiliary functions with a rectangular thermostat.
As one would expect for such a ubiquitous device, thermostats are used by people with a wide range of physical abilities including those with vision limitations. Such people find most common thermostats difficult to operate because the temperature setting is not discernible by them, resulting in a trial and error process to achieve a comfortable setting. One exception to this is the Honeywell ROUND.RTM."Easy to Use" thermostat, which has an enlarged scale and knob to aid people with vision limitations. The adjustment mechanism also has a detent which makes it possible to set the thermostat by feel alone. Features of this thermostat are disclosed in U.S. Pat. Nos. 4,582,251 issued on Apr. 15, 1986 and 5,303,612 issued on Apr. 19, 1994, both to Odom et al.
There is a large demand for thermostats with these specialized features. This has led to the perceived need for a rectangular lever set thermostat which accommodates people with vision limitations.